This invention relates to sun tracking devices and more particularly relates to a sun tracking apparatus of system for mounting solar devices.
A solar tracking device is sometimes referred to as a sun follower and is a slowly rotating mechanism in which a specific surface or axis of the apparatus is maintained to always point toward the sun. These solar trackers or sun followers are used for a number of purposes, such as a heliostat, a solar heater or furnace, or with a solar panel for collecting the sun's energy. A heliostat is a mechanism containing a rotating flat mirror capable of directing the sun's rays at some fixed point. A solar heater or furnace is an apparatus in which a lens or parabolic reflector is rotated, usually around its focal point so as to maintain its optical axis pointing toward the sun. Solar panels can be any type of device for collecting the sun's energy, such as solar cells, sensors, or other instruments whose surface is maintained perpendicular to the sun's rays.
Heliostats are particularly useful for applications in the areas of residential and industrial illumination, spectacular light show displays, for intense or concentrated lighting or illumination for solar power generation, and as a scientific tool in the general field of solar experimentation. For solar power generation, "solar farms" may be constructed containing large arrays of heliostats.
There are two common types of mounting configurations for these solar tracking devices. These are the horizon mount and the equatorial mount. One type of device which most frequently uses the horizon mount is a sun tracker having a servo-driven rotatable platform. This is usually an arrangement having two axes of rotation. A main yoke rotates in azimuth with its axis perpendicular to a horizontal plane, while the inner gimbal has its axis in the horizontal plane and rotates vertically in elevation. Each axis will be driven by an independent servo or torque motor and each motor receives its drive command from an independent axis oriented solar sensor which may be a photocell sensitive to light or a thermal-type sensor. This two-axis rotational system is operated by producing a null whenever the yoke and gimbal are pointed directly at the sun's rays. There are, however, several disadvantages to this system. One of these is that a high-speed, high-torque motor is required for each axis. Another disadvantage is that a complicated closed-loop, sensing control drive system (with damping) is required for each motor. A further disadvantage is that high acceleration rates can be encountered whenever the platform slews to follow a randomly shadowed sun.
The so-called equatorial mount device is also a two-axis yoke and gimbal. However, in this device the axis of the main yoke is oriented parallel to the earth's rotational axis. In this device a rotation around the polar axis counter to the earth's rotation will cause the main yoke to follow the sun's diurnal motion, a rotation which is essentially linear in time. For this reason a clock motor is most often used to drive this axis. The inner gimbal can be kept pointing directly at the sun by making it rock back and forth sinusoidally once per year to a maximum angular offset of plus or minus 231/2.degree., which is equal to the obliquity of the ecliptic. This means the inner gimbal rotates on the declination axis only a small amount each day; therefore, this adjustment is frequently done manually every day or so. While manual adjustment every day or so is relatively economical, it certainly is not very convenient. Mechanization of the declination adjustment can be made by installing a second, one-revolution-per-year motor on the main yoke with appropriate levers to tilt the inner gimbal back and forth the appropriate amount. However, as with the horizon-mounted servo system, this yields a two-motor device which is further complicated by the necessity for slip rings with the second motor. Another method of mechanizing the declination adjustment is by gearing down the main drive to one revolution per year and coupling the declination of the inner gimbal to it. This technique is described in U.S. Pat. No. 3,656,844, issued Apr. 18, 1972, to Botskor, for a sun-following device. The difficulty with the device disclosed in this patent is that it is extremely complicated and does not appear to accurately follow the sun.